The present invention relates to a conjugated polymer and uses thereof such as in an optical device, and to a process for preparing such a polymer.
Organic electroluminescent devices which use an organic material as the light-emissive material are known in this art. Among organic materials, simple aromatic molecules such as anthracene, perilene and coronene are known to show electroluminescence. U.S. Pat. No. 4,539,507 discloses the use of small molecule organic materials as the light-emissive material, for example, 8-hydroxy quinoline (aluminium). PCT/WO90/13148 discloses an electroluminescent device comprising a semiconducting layer comprising a polymer film as the light-emissive layer which comprises at least one conjugated polymer. In this case, the polymer film comprises a poly(para-phenylene vinylene)(PPV) film.
It is known to use a semiconductive conjugated co-polymer as the light-emissive layer in an electroluminescent device. The semiconductive conjugated copolymer comprises at least two chemically different monomers which, when existing in their individual homopolymer forms, typically have different semiconductor bandgaps. The proportion of the chemically different monomer units in the copolymer can be selected to control the semiconductor bandgap of the copolymer so as to control the optical properties of the copolymer. The extent of conjugation of the copolymer affects the nxe2x80x94n* bandgap of the copolymer. This property may be exploited so that the semiconductor bandgap is modulated to control the wavelength of radiation emitted during luminescence. In addition, by modulating the semiconductor bandgap of the copolymer it is possible to increase the quantum efficiency of the copolymer when exited to luminesce. Furthermore, the semiconductor bandgap is a factor affecting the refractive index of the copolymer.
A method of preparation for aryl-containing conjugated polymers is the Suzuki reaction. U.S. Pat. No. 5,777,070 is directed to attempts to improve the Suzuki reaction to form conjugated polymers from aromatic monomers. The process involves contacting (i) monomers having two reactive groups selected from boronic acid, C1-C6 boronic acid ester C1-C6 borane and combinations thereof with aromatic dihalide functional monomers or (ii) monomers having one reactive boronic acid, boronic acid ester or borane group and one reactive halide functional group with each other. Various aromatic monomers are proposed including those containing triarylamines.
A triarylamine unit has the general structure Ar1Ar2Ar3N where each Ar is the same or different and is an aryl or heteroaryl group.
U.S. Pat. No. 5,633,337, U.S. Pat. No. 5,536,866 and U.S. Pat. No. 5,534,613 each discloses a polymer which comprises triarylamine units. In these polymers, a repeat unit can be defined which comprises a heteroaryl group. However, the heteroaryl group is not directly linked to a nitrogen group. Instead, the heteroaryl group is indirectly linked to a nitrogen group via a phenylene group. In each of these three documents this is an essential feature of the described polymer structure. This structure is essential for achieving the advantageous properties of the described polymers.
U.S. Pat. No. 5,814,244 is concerned broadly with an electroluminescence material comprising one or more polymers which comprise structural units of the formula: 
where the symbols and indices have the following meanings:
Ar1, Ar2, Ar3, Ar4, Ar5, Ar6 are identical or different, monocyclic and/or polycyclic aryl and/or heteroaryl groups which may be linked via one or more bridges and/or be condensed and may be unsubstituted or substituted, where Ar1, Ar3, Ar5 and Ar6 are each divalent and Ar2 and Ar4 are each monovalent;
R1 is H, a hydrocarbon radical having from 1 to 22 carbon atoms, which may be unsubstituted or substituted, preferably by F, and can also contain heteroatoms, preferably 0, or Ar, where Ar7 is, independently of Ar1-6, as defined for Ar1-6;
n is 0, 1 or 2.
The polymers disclosed in this document have low molecular weight and, thus, would have relatively low processability. The presence of vinyl groups in the polymer makes the polymer relatively unstable. The polymers disclosed in this document are not end-capped.
In view of the prior art, there still remains a need for providing new polymers suitable for use in optical devices, particularly electroluminescent devices.
The present invention aims to provide such a new polymer.
Accordingly, in a first aspect, the present invention provides a polymer which comprises triarylamine units. The polymer comprises one or more structural units comprising Arh-NAr2 where N is directly linked to Arh and in which each Ar is the same or different and comprises a substituted or unsubstituted aryl or heteroaryl group and N is directly linked to Arh.
FIG. 1 shows the structure of an exemplary optical device, which contains layers comprising polymers in accordance with an invention.
It has been found that incorporation of triarylamine units into polymers according to the present invention provides materials with the attractive physical and processing properties of polymers and the ability in their synthesis to select the aryl or heteroaryl groups and their substituents so as to modulate the bandgap of the polymers. This is an important feature, particularly in the design of electroluminescent devices whose efficiency can depend upon the matching of the highest occupied molecular orbital and lowest unoccupied molecular orbital levels of the polymer with the cathode and anode and device host material.
For the purposes of the present invention, the term xe2x80x9cpolymerxe2x80x9d should be interpreted as including linear and branched polymers, oligomers, dendrimers, homopolymers, copolymers and terpolymers.
Preferably, Arh comprises a substituted or unsubstituted nitrogen-containing heteroaryl group. Generally, the heteroaryl group should comprise an electron-deficient heteroatom.
Preferably, each Ar is a substituted or unsubstituted phenyl group. Where the phenyl group is unsubstituted, the polymer is an oligomer. Where the phenyl group is substituted, substituents may be of a nature so as simply to build up the polymer chain and/or to control the bandgap of the polymer or to confer on the polymer solubility in a particular solvent system. Typical solvents include non-polar solvents. For these purposes it is preferred that the polymer bears one or more substituents.
In a first embodiment, the polymer comprises a linear polymer in which the or each structural unit comprises Arh (NAr2) Arco, wherein Arco comprises a substituted or unsubstituted aryl or heteroaryl group, Arh comprises a substituted or unsubstituted heteroaryl group and each Ar is the same or different and comprises a substituted or unsubstituted aryl or heteroaryl group. It is preferred that Arco is different from Arh. As discussed above, a substituent on Arco can modulate the semiconductor bandgap of the polymer.
The copolymer where the polymer backbone contains one or more divinylenearylene units may be excluded from the scope of the present invention. Furthermore, a homopolymer where the backbone contains one or more divinylenearylene units can be excluded from the present invention. Generally, this copolymer and this homopolymer are not excluded from the present invention.
In a first aspect of the first embodiment it is preferred that Arh is pendent from the polymer backbone.
In a first subgroup of the first aspect of the first embodiment it is preferred that the polymer comprises a plurality of structural units, having a formula as shown in formula (13): 
Most preferably in this first subgroup, the polymer comprises a plurality of structural units, having a formula as shown in formula (8): 
In formulae (13) and (8) above, Arh preferably comprises a group as shown in any one of formulae (1) to (4): 
In a second subgroup of the first aspect of the first embodiment, it is preferred that the polymer comprises a plurality of structural units having a formula as shown in formula (14): 
where Arh may be further substituted. Increasing the number of substituents on Arh is one way of increasing the solubility of the polymer.
Most preferably in this second subgroup the polymer comprises a plurality of structural units, having a formula as shown in formula (15): 
Other substituents can be used on the triazine ring. These substituents modulate the bandgap of the polymer and alter the charge transport properties of the polymer.
Conveniently, the triazine ring is stable and is easily substituted. However, groups such as any isomer of diazine or pyridene could be used in place of the triazine ring.
A polymer comprising a repeat unit having a formula as shown in one of formulas (8), (13), (14) or (15) may comprise a copolymer or co-oligomer. Alternatively, the polymer may comprise a homopolymer or homo-oligomer that is made from a single type of monomer. In this regard a monomer is distinguished from a repeat unit in so far as a homopolymer, for example (AB)n may be defined as having one or more different repeat units (i.e. a single repeat unit AB, or a repeat unit A and a repeat unit B).
A typical process for preparation of a polymer according to the first subgroup of the first aspect of the first embodiment is as follows. 
In the above reaction scheme, each Hal is preferably Br. The conditions in step 3 are any conditions under which the reactants polymerise such as under Suzuki polymerisation conditions which may typically involve the use of a palladium catalyst. Step 1 is typically a palladium or copper coupling reaction where the starting material, ArhNH2, is reacted with iodobenzene or bromobenzene Step 2 is a halogenation reaction.
Where Arh comprises a group as shown in any one of formulae (1) to (4), ArhNH2 as referred to in the above reaction scheme may be: 
In a second aspect of the first embodiment, Arh forms a part of the polymer backbone. In this second aspect, it is preferred that Arh comprises an amino substituted heteroaryl group, more preferably, an amino substituted heteroaryl group having formula (5): 
In the second aspect of the first embodiment, it is preferred that Arco is a substituted or unsubstituted phenyl group. Arco is chosen having regard to steric hinderance and possible twisting of the polymer chain with a view to controlling the extent of conjugation of the polymer.
In the second aspect of the first embodiment, it is further preferred that Arco is pendent from the polymer backbone, in this regard, it is still further preferred that the or each structural unit comprises a group having formula (11): 
where Arh, Arco are as defined above and (Ar2N) is the same or different from (NAr2).
Preferably, (NAr2) and (Ar2N) are the same. More preferably, (NAr2) and (Ar2N) each comprise a group having general formula (9) that is substituted or unsubstituted: 
Advantageously, in the first embodiment of this invention, the or each structural unit is a repeat unit in the present polymer. Preferred structural units that are each a repeat unit according to the second aspect of the first embodiment are shown by Formulae (12a) and (12b) and (16a) and (16b): 
where R, R1, R2 and R3 are the same or different and each R is a substituent group, preferably hydrocarbyl, optionally containing one or more heteroatoms, more preferably aryl, alkyl, heteroaryl, heteroalkyl, arylalkyl, aromatic or heteroaromatic.
Preferably, R and Rxe2x80x2 are the same.
A particular structural unit that is a repeat unit of interest having formula (12) is shown by Formula (13): 
The present inventors envisage that a homopolymer comprising a repeat unit having general formula (12), (13) or (16) would be useful as an electron transport material in an optical device, particularly an electroluminescent device.
Also, reference is made to International patent publication No. WO/0055927 the contents of which are incorporated herein by reference. Repeat units according to the present invention such as those having general formula (12), (13) or (16), particularly general formula (12), are envisaged to be useful as charge (hole or electron) transporters and/or as emitters in polymers according to WO/0055927.
The first steps in a typical process for preparing a polymer comprising a structural unit or repeat unit having formula (12) or (13) are shown below: 
Product 12a or 12b then can be used in any suitable polymerisation reaction to obtain a polymer according to the second aspect of the first embodiment.
In the above reaction scheme, each Hal is preferably Br.
A preferred polymer in accordance with the second aspect of the first embodiment is a copolymer. Such polymers are envisaged as being useful for transporting electrons when used in an optical device, particularly an electroluminescent device. At the same time as being capable of transporting electrons, such polymers also may be capable of transporting protons and/or combining protons and electrons so as to generate light.
It is preferred that a polymer according to the first or second aspect of the fist embodiment is at least 100, preferably at least 105, monomers in length. A typical upper limit for the polymer length is about 300 monomers, although the length could be up to 1000 monomers.
In a second preferred embodiment, the polymer comprises a dendrimer comprising an initiator core or core unit and branch units. Preferably, the one or more structural units comprises a core unit. Most preferably, the polymer has a single structural unit.
According to the second embodiment, the dendrimer more preferably comprises a branch unit, specifically one type of branch unit, the most preferred branch unit being as shown in formula (9) which is substituted or unsubstituted. 
Preferably the dendrimers according to the second embodiment of the present invention are from 1st to 10th generation dendrimers.
In a first aspect of the second embodiment, one or more structural units comprises Arh(NAr2)3, where each N is directly linked to Arh and each (NAr2) is the same or different. Preferably, each (NAr2) is the same and is a substituted or unsubstituted phenyl group. As discussed above, each (NAr2) is chosen so as to control the bandgap of the polymer.
It is preferred that, in the first aspect of the second embodiment, Arh comprises a group as shown in formula (5): 
In the most preferred first aspect of the second embodiment, the polymer comprises a single structural unit comprising a group as shown in formula (6): 
where the structural unit comprises the core unit.
In a second aspect of the second embodiment, the structural unit comprises Arh(NAr2)2Arxe2x80x3, where Arxe2x80x3 is a substituted or unsubstituted aryl or heteroaryl group and each (NAr2) is the same or different. Preferably, as in the first aspect of the second embodiment, each (NAr2) is the same and is a substituted or unsubstituted phenyl group.
Preferably, Arxe2x80x3 is a substituted or unsubstituted phenyl group. Arxe2x80x3 should be chosen having regard to steric hinderance and possible twisting of the polymer chain with a view to controlling the extent of conjugation of the polymer.
In a most preferred embodiment of the second aspect of the second embodiment, the polymer comprises a single structural unit comprising a group having the formula as shown in formula (7): 
where the single structural unit comprises the core unit.
A typical process for preparation of a polymer according to the first aspect of the second embodiment involves melamine as a starting material. This may be subjected to a palladium coupling reaction with iodobenzene or bromobenzene to produce a structure as shown in formula (10): 
Further generations of the dendrimer may be built by subjecting the compound having formula 10 to one or more cycles of halogenation, preferably bromination, followed by a reaction with (Ph)2NB(OH)2, under appropriate conditions. This may conveniently be carried out using a Suzuki reaction. A corresponding process may be used to prepare a polymer according to the second aspect of the second invention where 2,4,diamino-6-phenyl-1,3,5-triazine (a melamine derivative) is used in place of the melamine starting material.
In the second embodiment, the core unit may comprise a structure as shown in formula (6) or (7). In the polymer, linear repeat units such as those shown in formula (12) or (15) may be attached to the core unit. Such polymers may be defined as xe2x80x9clinearxe2x80x9d but dendrimeric. These polymers are envisaged to be useful as charge (electron or hole) transport materials and/or as emissive materials.
Such a polymer preferably is at least 100, preferably at least 150, monomers in length. A typical upper limit for the polymer length is about 300 monomers, although the length could be up to 1000 monomers.
In a further aspect, there is provided use of a polymer according to the first or second embodiment of the present invention in an optical device such as a luminescent device, preferably an electroluminescent device. Other devices include photoluminescent devices, photovoltaic devices and waveguides. Uses include the use of the polymer as an emissive material, a hole transporter or an electron transporter, typically in an electroluminescent device. The polymers may also be used in a dye composition, in a fiber or in a sensor.
In the present invention, there is further provided an optical device comprising a substrate and a composition supported by the substrate, which composition comprises a polymer according to the present invention. The substrate may itself be an electrode or any other type of substrate suitable for supporting the composition. The composition may include various layers such as an emissive layer optionally in contact with one or more hole and/or electron-transporting layer. Where the optical device comprises an electroluminescent device, the composition includes an electroluminescent emissive layer which may be the polymer or another emissive polymer.
A typical electroluminescent device will have an anode layer, a cathode layer and a light-emissive layer situated between the anode and the cathode. Optionally, a charge transport layer may be situated between the anode and/or the cathode and the light-emissive layer.
A blend of materials including a polymer according to the present invention may be used as the light-emissive layer in an electroluminescent device. Preferably, the polymer according to the present invention is blended with one or more hole and/or electron-transporting materials, even more preferably hole and/or electron-transporting polymers.
Alternatively, the polymer according to the present invention may be blended with an electroluminescent material, preferably any electroluminescent polymer.
Several different polymerisation methods are known which may be used to manufacture polymers in accordance with the present invention.
One particularly suitable method is disclosed in International patent publication No. WO 00/53656, the contents of which are incorporated herein by reference. This describes the process for preparing a conjugated polymer, which comprises polymerising in a reaction mixture (a) an aromatic monomer having at least two reactive boron derivative groups selected from a boronic acid group, a boronic ester group and a borane group, and an aromatic monomer having at least two reactive halide functional groups; or (b) an aromatic monomer having one reactive halide functional group and one reactive boron derivative group selected from a boronic acid group, a boronic ester group and a borane group, wherein the reaction mixture comprises a catalytic amount of a catalyst suitable for catalysing the polymerisation of the aromatic monomers, and an organic base in an amount sufficient to convert the reactive boron derivative functional groups into xe2x80x94BX3 anionic groups, wherein X is independently selected from the group consisting of F and OH.
Polymers according to the present invention which have been produced by this method are particularly advantageous. This is because reaction times are short and residual catalyst, e.g. palladium, levels are low.
This polymerisation method allows good control of the molecular weighs of the polymer. In part this is because this polymerisation method gives rise to few side reactions which means that polymers having a high molecular weight, for example, more than 100 or 150 repeat units and up to 300 repeat units or 1000 repeat units, may be obtained.
It should be noted that polymers according to the present invention may be end-capped to remove the halogen end-groups. This end-capping, for example by the addition of halobenzene or phenyl boronic acid. This is exemplified in Example 3(ii).
Another polymerisation method is disclosed in U.S. Pat. No. 5,777,070, The process involves contacting monomers having two reactive groups selected from boronic acid, C1-C6 boronic acid ester, C1-C6 borane and combinations thereof with aromatic dihalide functional monomers or monomers having one reactive boronic acid, boronic acid ester or borane group and one reactive halide functional group with each other.
A further polymerisation method is known from xe2x80x9cMacromoleculesxe2x80x9d, 31, 1099-1103 (1998). The polymerisation reaction involves nickel-mediated coupling of dibromide monomers. This method commonly is known as xe2x80x9cYamamoto Polymerisationxe2x80x9d.